Method and apparatus for explosively forming article of relatively brittle metal



Dec- 3, 1968 l. LIEBERMAN ET AL 3,413,833

METHOD AND APPARATUS FOR EXPLOSIVELY FORMING ARTICLE OF RELATIVELY BRITTLE METAL Filed March 9, 196e INVENTORS IRVING LIEBERMAN LOUIS ZERNOW LOUIS H. KNOP MQW ATTORNEY United States Patent 3,413,833 METHOD AND APPARATUS FOR EXPLOSIVELY FORNIING ARTICLE F RELATIVELY BRITTLE METAL llrving Lieberman, Covina, and Louis H. Knop and Louis Zernow, Glendora, Calif. assignors to Aerojet-General Corporation, El Monte, Calif., a corporation of Ohio Continuation-impart of application Ser. No. 304,922, Aug. 27, 1963. This application Mar. 9, 1966, Ser. No. 536,559

8 Claims. (Cl. 7256) ABSTRACT 0F THE DISCLOSURE This disclosure concerns a method and apparatus for forming workpieces having either a tubular or a flat configuration and being of a relatively brittle metal into shaped articles by vutilizing the energy generated from the detonation of an explosive charge. The method relies upon the use of a body of molten metal as a medium for heating the relatively brittle metal workpiece which decreases the brittle characteristics of the metal prior to the detonation of the explosive charge and as a shock transmitting medium through which the energy from the detonated explosive charge is directed to the workpiece. The explosive energy forces the workpiece against a contoured die, thereby causing the workpiece to conform to the shape of the die surfaces to produce a shaped article without shattering or fragmentation of the relatively brittle metal from which it is made.

This invention is a continuation-in-part of our copending application Ser. No. 304,922, filed Aug. 27, 1963, now abandoned.

The present invention relates to a method of forming by pressure and more particularly to such a method wherein the pressure is derived from the energy released by a detonated explosive.

Many materials, such as tungsten, are highly brittle at ambient temperatures. This characteristic poses a problem when it is desired to form a specimen of desired shape from such materials because they are likely to shatter or fragment. Our method was developed to overcome this problem which was heretofore not adequately soluble.

It is, therefore, an object of our invention to provide a method whereby materials, which are highly brittle, may be formed into desired shapes.

It is another object of our invention to form and to shape materials by explosive pressure.

A further object is to apply heat to the materials before being deformed by explosive pressure.

Other aims and objects of our invention will appear from the following explanation thereof:

In carrying out our method, a workpiece, composed of a material which is brittle at normal temperatures, is disposed in or on a die containing the shape or impression desired to be transferred to the workpiece. The workpiece is then heated as by a molten or heated substance to decrease its brittle characteristics. An explosive charge is placed adjacent to or within the substance which is now arranged between the workpiece and the charge. lUpon detonation of the charge, the detonation wave generates a pressure which is transmitted by and through the substance to force the workpiece against the die, thereby causing the workpiece to conform to the shape of the die.

For a more complete understanding of our invention, reference is made to the following explanation and the accompanying drawings in which:

FIG. 1 is a vertical cross-section of a Set-up suitable 3,413,833 Patented Dec. 3, 1968 lCe for producing a specimen taken on the line 1--1 in FIG. 2;

FIG. 2 is a top plan view of the apparatus shown in FIG. l;

FIG. 3 is a vertical section of apparatus designed to produce another specimen;

FIG. 4 is a vertical section of apparatus for producing a further specimen; and

FIG. 5 is a sectional view of the specimen produced by the apparatus shown in FIG. 4.

Referring now to FIG. l, a die holder comprises a base plate 11 and a circular wall 12 secured thereto at its foot. A die formed from halves 13 and 14 is nested inthe holder. A workpiece such as a tube 15 of high melting point metal, e.g. tungsten, which melts at 3500 C., is arranged within the die and rests on base plate 11.

A container 16 for molten metal 17 is disposed within the workpiece and may be formed of copper, whose melting point is 1083 C. The molten metal may be aluminum, which has a melting point of 660.2 C. The metal is not poured into the container until immediately before the forming operation.

Explosive charge 18 such as P.E.T.N. or RDX formed as a stick is inserted centrally into the molten metal also immediately before the forming operation is to be performed. A detonator 21 and electrical leads 22 are fitted to the stick or rod comprising the explosive 18 for achieving the detonation thereof when actuated. The charge is clad in a heat insulating material such as a sheath of woven asbestos.

Because the explosive must be accurately centered in the molten heating metal, it is `secured to a metal rod 19 by thin metal bands 20. The rod also affords suicient weight to enable the explosive to be quickly lowered into position.

When explosive 18 is detonated, the heated workpiece is forced by the explosive energy against the inner surface of the die to fashion a specimen. The molten Ialuminum and container 16 meanwhile are, at least partially, vaporized or disintegrated.

FIG. 3 shows apparatus arranged for executing the method. In this figure, a bowl-shaped specimen is formed in a die 24, which in this case does not need to be segmental, from a tubular blank 23 of high melting point metal. The blank or workpiece is positioned on the at bottom of the die and -a countainer 25 for a molten heating substance or medium is disposed within the workpiece. An explosive charge 26, which is wrapped in a heat insulation sheath 27 and contained in a shatterable tube 28 of heat resistant material, such Ias Pyrex, is secured to the end of a metal rod 19a. The explosive 26 is tted with a detonator 29 to be fired electrically through a cable 30 from a control booth (not shown).

Rod 19a is supported by a cable 31 4running over pulleys 32 and 33. The pulleys are mounted on a standard 34 carried for swinging movement in a horizontal plane about a vertical support 35. The rod is guided for accurate vertical movement by a tubular guide 36 secured to the standard.

The effect of detonating the explosive 26 is the same as previously described with respect to the embodiment shown in FIGS. 1 and 2'.

The method of the invention can also be carried out, if preferred, by pouring the molten heating medium from any suitable heating furnace through pouring spouts -directly into a positioned workpiece which doubles then as a container.

FIG. 4 shows a further modification for effecting our novel method. In this embodiment, the medium serving both to heat the work and to distribute `the energy of explosion to the workpiece is a deformable solid, `such as lead. A die 40 comprises a body 41 and a container section 42. A workpiece 39 is provided with a contour to lit within the body. A lead block 43 is positioned while cold, if desired, within section 42 which is screwed onto body 41. The block is then heated to a point below its melting point by electrical resistance units 44 inserted in slots 45 of the container section.

Alternatively, the workpiece may lirst be heated to a high temperature, such as by the application of flame directly on the tungsten workpiece. Then, the explosive and lead block are lowered onto the hot workpiece just prior to forming. An explosive 48 is positioned above the lead block 43. The explosive 48 is equipped with a detonator 49 having electrical leads 47 for achieving actuation thereof.

Upon explosion of charge 48, the energy generated thereby is transmitted through the solid lead block, or molten liquid lead to the workpiece to force it into the die. A specimen 38 shown in PIG. 5 is produced thereby.

The method of the invention may also be employed for the explosive compaction of powders, Where elevated temperatures are desired, by using a medium both to heat the work and to transmit the energy of an explosive placed in contact 4with the medium. Thus, when the body of explosive is detonated, the powder is further heated, subjected to pressure, and compacted into desired shape.

Preferred embodiments of the method and means of the invention have been described and shown by way of illustration, but not as limitative of the scope of the invention, since those skilled in the art may ellect modifications in said method and means without departing from the scope of the invention as defined by the appended claims.

We claim:

1. Method of explosive forming of a relatively high melting point metal blank, comprising the steps of:

(a) placing one surface of the metal blank over a forming surface of a die;

(b) positioning a body of soft metal in contact with and extending over another surface of the metal blank, while maintaining the body free from contact with the die;

(c) raising the temperature of the soft metal body to bring it to a liquid condition;

(d) moving an explosive charge into Contact with the molten soft metal; and

(e) detonating the explosive charge, thereby transmitting energy from the detonating explosive charge through the molten soft metal against the blank and forming it onto the forming surface of the die.

2. Apparatus for explosive forming yof a tubular metal workpiece, comprising:

(a) a die having forming surfaces arranged in surrounding relationship to the tubular workpiece;

(b) a container having wall surfaces for being received within the tubular workpiece, the wall surfaces being disposed in close proximity to the inner Walls of the tubular workpiece;

(c) a body of liquid material at an elevated temperature disposed within said container for raising the temperature of the tubular workpiece by heat conduction through the walls of the container; and

(d) an explosive charge submerged within the liquid material, whereby upon detonation of the explosive charge, explosive deformation of the tubular workpiece occurs, shaping it in accordance with the geometry of the forming surfaces of the die.

3. Apparatus as in claim 2, in which the liquid material comprises metal having a relatively low melting point.

4. Apparatus for explosive forming of a sheetlike metal workpiece, comprising:

(a) a die having a forming surface disposed adjacent and in opposed relation to a surface of the workpiece to be formed thereagainst;

(b) a body of material having a relatively low melt- Cil ing point, said body of low melting material initially being in the solid state and being disposed in contacting relation to portions of the workpiece other than the surface opposed to the forming surface of the die (c) heating means operatively related to the body of low melting material;

(d) an explosive charge arranged in contacting relation to the body of low melting material;

(e) means for actuating the heating means to melt the body of low melting material and raise the temperature of the workpiece; and

(f) means for detonating the explosive charge after the workpiece has been heated, whereby the explosive energy from the detonating explosive charge is transmitted through the molten body of low melting material to form the heated workpiece against the forming surface of the die.

5. The method of explosive forming of high melting point metals comprising the steps of:

(a) placing a tubular workpiece made of metal having a high melting point within a die having surfaces to which the tubular workpiece is to be conformed;

(b) positioning a body of liquid material at an elevated temperature within and substantially filling said tubular workpiece;

(c) heating said tubular workpiece by the body of liquid material at an elevated temperature to raise the temperature of said tubular workpiece to a point below its melting point but high enough to substantially decrease any brittle characteristic of the metal from which the tubular workpiece is made;

(d) placing an explosive charge substantially centrally within and in submerged relation to the body of liquid material at an elevated temperature; and

(e) detonating the explosive charge, whereby the energy from the detonating explosive charge is transmitted through the body of liquid material to the heated tubular workpiece, forcing the tubular workpiece against the surfaces of the die and conforming the tubular workpiece thereto.

6. The method as in claim 5, in which the body of liquid material at an elevated temperature which is positioned within and substantially filling said tubular Workpiece is molten metal havingr a melting point lower than the metal of the tubular workpiece.

7. The method as in claim 5, wherein positioning of the body of liquid material at an elevated temperature within and substantially lilling said tubular workpiece is accomplished by (a) initially disposing a container made of a material having a melting point higher than the temperature to which the body of liquid material is elevated within the tubular workpiece in close proximity to the interior surface thereof; and

(b) filling the container with the body of liquid material at an elevated temperature; and

(c) the heating of said tubular workpiece by the body of liquid material at an elevated temperature being achieved by transmitting heat from the body of liquid material to the tubular workpiece through` the container.

S. The method of explosive forming of high melting point metals comprising the steps of:

(a) placing one surface of a workpiece made of metal having a high melting point yover a forming surface of a die;

(b) providing a body of liquid material at an elevated temperature in close proximity to and extending over another surface of the workpiece, while maintaining the body of liquid material free from contact with the die;

(c) heating said workpiece by the body of liquid material at an elevated temperature to raise the tem- 5 6 perature of said workpiece to a point below its forming surface of the die and conforming the workmelting point but high enough to substantially depiece thereto. crease any brittle characteristic of the meal from which the workpiece is made; References Cited (d) disposing an explosive charge in operative relation 5 to the body of liquid material at an elevated tem- UNITED STATES PATENTS perature; and 2,770,874 ll/ 1956 Lindow 29-421 (e) detonating the explosive charge, whereby the en- 3,036,373 5/ 1962 Drexelius 72-56 ergy from the detonating explosive charge is trans- 3,126,623 3/1964 Merrill 29-421 mitted through the body of liquid material to the 10 heated workpiece, forcing the workpiece against the RICHARD J. HERBST, Primary Examiner. 

